WPF - Tooltip minor cleanup

- Ignore tooltip change if both new/old values are null/empty
- Change order so timer is stopped before hiding tooltip

Author: amaitland

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -1609,14 +1609,21 @@ protected virtual void OnTooltipTextChanged(string oldValue, string newValue)
                 return;
             }
 
-            if (string.IsNullOrEmpty(newValue))
+            // There are cases where oldValue is null and newValue is string.Empty
+            // and vice versa, simply ignore when string.IsNullOrEmpty for both.
+            if (string.IsNullOrEmpty(oldValue) && string.IsNullOrEmpty(newValue))
             {
-                UiThreadRunAsync(() => OpenOrCloseToolTip(null), DispatcherPriority.Render);
+                return;
+            }
 
+            if (string.IsNullOrEmpty(newValue))
+            {
                 if (timer.IsEnabled)
                 {
                     timer.Stop();
                 }
+
+                OpenOrCloseToolTip(null);
             }
             else if (!timer.IsEnabled)
             {
@@ -2145,7 +2152,10 @@ protected virtual void OpenOrCloseToolTip(string text)
         {
             if (string.IsNullOrEmpty(text))
             {
-                toolTip.IsOpen = false;
+                if (toolTip.IsOpen)
+                {
+                    toolTip.IsOpen = false;
+                }
             }
             else
             {